Photometry and Spectroscopy of KS Ursae Majoris during Superoutburst

We report photometric and spectroscopic observations of the SU UMa-type dwarf novae, KS Ursae Majoris, during its 2003 February superoutburst. Modulations with a period of 0.07017 ± 0.00021 day, which is 3.3% larger than the orbital period, have been found during the superoutburst and may be positive superhumps. A maximum trough-to-peak amplitude of around 0.3 magnitude is determined for this superhump. The spectra show broad, absorption-line profiles. The lines display blue and red troughs which alternate in depth. The radial velocity curve of the absorption wings of Hβ has an amplitude of 40±11 km s and a phase offset of 0.12±0.03. The γ velocity of the binary is 3 ± 9 km s and varies on an order of 50 km s from day to day. From another clear evidence for a precessing eccentric disk, we obtain a solution to an eccentric outer disk consistent with theoretical works, which demonstrates the validity of the relation between superhumps and tidal effects. The inner part of the disk is also eccentric as evidenced by asymmetric and symmetric wings in the lines. Therefore, the whole disk is eccentric and the variation of γ velocity and the evolutionary asymmetric line profiles could be criterions for an precessing eccentric accretion disk. Subject headings: accretion, accretion disks —binaries: close— novae, cataclysmic variables — stars: dwarf nova — stars: individual (KS Ursae Majoris)